I encountered issues with powerplay not working where no active clock shows in pp_dpm_*, and I get powerplay "failed to send message" errors.

I tried various kernel versions up to 4.14.5, different module parameters like ppfeaturemask=1, I upgraded the motherboard BIOS, and tried different VGA BIOS versions on the cards.

After 2 days of experimenting, I figured out that powerplay won't work with a card plugged into the 16x motherboard slot. When I plug 1 or more cards into the 1x slots using 16x-1x risers, powerplay works fine.

I also have an Asus z87 motherboard, and Tonga cards work fine in the 16x slots on that board with AMDGPU-PRO 17.40 and kernel 4.10.5.